1. Field of the Invention
The present invention relates to carbon materials and methods of manufacturing, and specifically to carbon materials suitable for use in electrodes and other components used in high energy density storage devices, such as electric double layer capacitors.
2. Technical Background
High density energy storage devices, such as electric double layer capacitors, have been the subject of considerable research. An electric double layer capacitor or EDLC is a type of capacitor that typically consists of carbon electrodes separated by a porous separator, current collectors, and an electrolyte solution. When an electric potential is applied to an EDLC, ionic current flows due to the attraction of anions to the positive electrode and cations to the negative electrode. This ionic current flow generates an electric charge that is stored at the interface between each polarized electrode and the electrolyte solution.
The design of an EDLC can vary depending on the intended application and can include, for example, standard jelly roll designs, prismatic designs, honeycomb designs, hybrid designs, or other designs known in the art. The energy density and the specific power of an EDLC can be affected by the properties of the components comprising the EDLC, including the electrode and the electrolyte utilized. With respect to the electrode, high surface area carbons, carbon nanotubes, other forms of carbon, and composite materials have been utilized in manufacturing such devices.
Conventional carbons for EDLC electrodes can be prepared from natural materials such as wood, charcoal and coal tar pitch, or from synthetic materials such as resins. Where synthetic precursors are utilized, the precursor is typically first crosslinked to solidify the precursor, carbonized in an inert atmosphere (such as nitrogen) and then activated. The activation is usually performed by heating the carbon at high temperatures (800-900° C.) in a partially oxidized atmosphere (such as carbon dioxide). During the carbonization/activation process, a large number of micropores are formed in the surface of the carbon material. These micropores increase the surface area of the carbon which results in increased capacitance. Other conventional carbons for electrodes can be formed from cured synthetic precursors that are treated with alkali or acids and then further treated at high temperatures to create porosity.
EDLC's incorporating carbon electrodes manufactured by such conventional processes usually have an energy density within the range of 6-7 Wh/l. However, this energy density range is not sufficient or practical for high energy applications, such as hybrid vehicles. Accordingly, a new carbon material for use with EDLC's suited for high energy applications is needed.
Thus, there is a need to address the aforementioned problems and other shortcomings associated with the traditional electric double layer capacitors. These needs and other needs are satisfied by the carbon compositions and methods of the present invention.